Interface Selection; Preventing Timeouts - Epson DFX-8500 Service Manual

DFX-8500

INTERFACE SELECTION

The printer has three interfaces: parallel, serial, and optional Type-B. These interfaces are selected
automatically or manually using DIP switches.


Manual selection:
One of three interfaces can be selected using DIP switches.


Automatic selection:
If the automatic interface is selected using DIP switch settings, the printer is initialized to an idle
state, scanning all interfaces to see which receives data first. The interface that receives data first
becomes active. When the host stops data transfer, and the printer is in stand-by state for the time
specified by the DIP switch settings, the printer returns to the idle state. As long as the host keeps
sending data or the printer interface is in a busy state, the selected interface remains selected.


Interface state and interface selection:
When the parallel interface is not selected, the interface enters a busy state.
When the serial interface is not selected, the interface sends the DTR signal MARK, X-OFF.
When the optional interface is not selected, the printer sends disable commands to the optional
interface.
When the printer is initialized or returned to the idle state, the parallel interface enters a ready state,
the serial interface sends DTR signal SPACE, X-ON, and the printer sends enable commands to the
optional interface.
Note: Interrupt signals (such as an /INIT signal for the parallel interface) are not effective while the
target interface is not selected.

PREVENTING TIMEOUTS

Hosts abandon data transfer to peripherals when a peripheral is in a busy state for some time. To prevent
hosts from timing out, the printer receives data very slowly, at a rate of several bytes per minute, even if the
printer is in a busy state. This slowdown begins when the input buffer grows to several hundred bytes.
Eventually, if the input buffer fills completely, the printer enters a continuously busy state.
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